If you want to measure the input impedance (S11) of the dipole, you'll have to use (or design) a balun. The dipole is a balanced antenna and cannot be measured as a single-ended device, e.g. a resistor, etc. Once the balun is ready, the "easiest" way is to design a TRL calibration kit and enter its data into the network analyzer.
Length[mts] = 0.95*(1/2)*300/f[MHz]
for a dipole in the "air"
For dipole in PCB(FR4 or close) I would say the
lenght could
Length[mts] = (α)(0.95)(1/2)(300)/(f[MHz])
where α is between 0.5 to 0.7 depending of the
dielectric.
Example: fo=2450 MHz(802.11), FR4(ε=3.48)-->α=0.66
Length[mts]= 0.66*0.95*0.5*300/2450 = 3.83 cm